I'm on the side of the split case theory - at least for now. To melt that much lead the powder must have ignited and discharged the gasses forward. If the powder ignited in a closed chamber the bullet would have left the case. This looks like burning powder without enough pressure to cause the bullet to exit. We all know that it takes very little pressure, say a primer charge with no powder, to push a bullet out of the case just to get stuck in the forcing cone or barrel. Defective bullet? I suppose that is possible, but seems rather unlikely. The most obvious answer is often the best. What does the brass look like?
Edit: Someone will probably refute this theory any minute, which will cause me to swear off giving my opinion on the forum after my first shot of Kentucky's finest - until next time
Edit #2 - I went back and read the OP. Funny smelling Bullseye? Hmmm?